Signal limiting device



July 4, 1933- w. L. CARLSON El AL 1,917,095

SIGNAL LIMITING DEVICE Filed Nov. 19, 1931 Fig.1. i g :5 5%.

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@ 31 nIUUh mar OUT PU 7' --AUDIO 5/GN4L IIYPUT- CARRIER FREQUENCY Inventor's: Wendell L..Ca\-lson, Ralph Sklolrnes, 1 M M Theirv Attorney.

: a-manual control. y 1 d i I "Heretofore means have been PI'OVlClGdfor I 7 responsively' to the intensity of' the received high frequency current to impress a vari able voltage upon the control element of one for JERSEY; nssieivons' T0 GENERAL i ELECTRIC} coMrn aconrormrron or lvnwyomgf Our invention; relates to signaling. systems and particularly to systems employing-high frequency currents, and has :for. one of its obects tov provide an lnexpenslve means for.

automatically maintaining; the intensity? of.

the signal output of a radio receiving eye tern below a predetermined level withoutthe use of-auxiliary equipment.

"It is well known thatwhen a high frequency receiving circuit is being adjusted: to receive a newly desired frequency, the signals; from a powerful or nearby station Will often be receive'diwith such great volume that the I detector is overloaded. Thisv overloadingdistorts the audio modulation and saturates the amplifier circuits at resonance so as to produce a double peaked tuning-.characteris-' tic. The volume will be greatly reduced at resonance due to saturati'onythus producing v anefiect similar to reducing the volume by limiting or controlling the transmissionlevel' in high frequency systems. These means have involved auxiliarytubes Which'operate V as shunt 'devices which tend to detune a poi"- ,tio of the tuned signaling circuit. Others have involved auxiliarytubes' fwhichoperate' more amplifier tubes to control the amplification of these tubes.

to maintain"the :.signal output of the re ceiverbelow a predetermined level, i

detector of radio receivers; which operates Without the necessity for auxiliary-equipment l r and which is simpleto construct and adjust; and which therefore may be applied toradio receivers'wit-hout material increasein the cost thereof. v ,7 I

In accordancew1th-;our1nvent1on, a resistance is'connected imheanode-cathode circuit;

Stillother' means have been provided which develop a potential." varying in accordance with the intensity of the varying-signal energy received, andlapply this potential to a control element of an ampli'fiertube to eliminatethe'efi'ects off'ading For the siGivALirMrT-ING ni v'r'cn V I ofa"detectorfto produce at direct current po w unmet-1 4mm; emmommmrmm fl s. iromvrns'or Hrinnoiv HEIGHTS} t tential" which is variablein response to the ntensityof the receiver signalcurrent; this potential being supplied to the; control. element of a ipreceding'ftube to limit the output thereofl so that the detector tube will not be 4 overloaded;

The nov'el features which we-believerto'be I V characteristicofour invention areset forth,

with particularity in; the appended, claims;

Our invention itself, however, both asto its 1 organization and method of operation, 'toi gether withfurtherzobjectsiand advantages '1 thereof, .7 will. be better. understood by. reference: to the. following:descriptionftaken in connection with} I the" accompany a drawing in in which Figulp-illustrates alpreferred rem- "bodime'ntof'our invention; and Fig; QshoWs the'eife'ct onithe output of adetector volumebecomes eXcessive;- 7 r drawing,v We

when the Q* Referring to Fig. 1 of i the have illustrated therein two detectors of a superheterodynej type of receiver, with an indication; that tin-intermediate frequency amplifier is interposed between i the two de-' tectors; The inputcircuitfl ris coupled to the igrida circuit 20f an electron discharge.

device '3 Ani oscillator: circuit 4 is coupled to theic'ircuits land 2; to provide the energy for beating with the incoming'signal energy to; produce .theinterrnediate frequency by' meansrof the firstdetector Theaoutp'utf* "circuit 5 of electron discharge. device 3 :is

coupled to the intermediate frequency ampli- V fier (-not vshownhflthe output of; which is coupled to; the grid circuit 60f the electron discharge device7 which operates asjthe sec ond; detectorqor demodulator. ;'lhe audio output of 'detectorZ is fed into transformer. 8

the secondarylof 'vvhich may be! connected to an audio amplifier or 'a suitable translating device. a

response to the intensity of the incoming purpose of develeping-a source of 7 direct current potential which is variable in 1 signal energy, we provide a resistor 9" between the'negati'v'e terminal of thesource of potenare:memes we a h d8; 1 vice 3 ;"and' a resistor 10 inseries -withre'sistor 9 and" connected between the: cathode of device 3 and the cathode of device 7. A resistor 11, of the type usually provided with power supply units, is shown tapped at an intermediate point to provide a potential for the screen grid electrode of electron discharge device 3.

The operation of this form of our invention is as follows: During normal operation of the circuit when the intensity of the received signal energy is below a certain predetermined level and reception is taking place in the usual way, the potentials developed across the resistors 9 and 10 are of an amount which will allow the detector devices S and 7 to operate in a normal way with a normal biasing potential. Assuming that a nearby station for which the manually operated volume control has'not been adjusted, is tuned in, or that for some other cause the intensity of the signal energy impressed upon the receiving circuit increases, an increase in the anode current of electron discharge detector 7 takes place, thus increasing the potentials developed across the resistors 9 and 10. An increase in the anode current of electron discharge detector 3 also takes place, which increases the potential developed across resistor 9, but the increase in potential due to this anode current increase is of a lesser magnitude than the increase in potential due to the increase in anode current from detector 7 and need not be considered. The increased potential developed by the increase in anode current in the detector 7' across resistor 9 further biases the control element of detector 8, thereby reducing the signal energy which is transferred to the intermediate frequency amplifier. This being the case, the signal energy to be amplified by the intermediate frequency amplifier will be greatly decreased and the signal energy impressed upon the detector 7 will not be of a value great enough seriously to overload the circuits. It is important that the potentials supplied to detector 3 initially are adjusted to produce but a small anode current so that the variations of anode current of detector 7 will predominate to control the grid bias of detector 3.

Fig. 2 illustrates the effect of impressing excessive signal energy upon the detector clevice 7, and illustrates the advantage resulting from our invention. Curve A shows the audio signal output of detector 7 of a system employing our invention plotted against the carrier frequency when the input of signal energy is controlled by the volume control. Curve B illustrates the double peak phenomenon in the tuning characteristic occurring in similar systems of the prior art when an excessive amount of signal energy is impressed upon the detector. The portion of the curve B between the peaks illustrates how the volume is reduced by saturation.

It is obvious that this phenomenon introduces distortion in the reproduced signals.

It may thus be seen that we have provided a volume control system which is simple in circuit structure and which does not involve additional electron discharge devices or circuits, and which operates directly in response to any increase in the received signal energy which exceeds a predetermined energy level..

Our invention has the further advantage that it does not involve mechanical moving parts which introduce undesirable efiects into the operation of the receiving system.

Our invention has the further advantage that it automatically prevents overloading the detector, thereby preventing the introduction of distortion.

While we have shown and described our. invention with particular reference to oertain specific receiving circuits, it will be apparent that it is not so limited and that it may be applied to other circuits as well. It. will also be apparent that the principles. herein disclosed'are susceptible of numerous other applications, and that modifications may bemade in the circuit arrangements and the instrumentalities employed without departing from the spirit and scope of our invention as set forth in the appended claims.

WVhat we claim as new and desire to secure by Letters Patent of the United States is:

1. In a radio receiving circuit, the combination including a heterodyne detector of the electron discharge type, and a second electron discharge detector, said detectors including cathode, anode and control elements, connections whereby current having amplitude variations dependent upon the characteristics of the transmission medium are supplied to said detectors, and means common to the cathode-anode circuits of both said detectors arranged to produce a source of direct current potential which is variable in response to the intensity of the received current and for supplying said potential to the control element of said hetero-. dyne detector thereby to control the output thereof in response to the intensity of the received current. I

2. A high frequency receiving circuit including an electron discharge device, a high frequency amplifier, an electron discharge detector, said electron discharge device and said electron discharge detector each including a cathode, an anode and a control element and connections whereby currents of different intensity are supplied to said electron discharge device, amplifier and detector, and means arranged in the cathode-anode circuits of said electron discharge device and said detector to produce a direct current potential which is variable in response to the intensity of the supplied current, and connections for impressing said direct current potential on thecontrol element of said electron discharge device thereby to maintain substantially constant the output of saidreceiving circuit.

p 3. In a radio receiving circuitythe combination of a-heterodyne detector comprising an electron discharge device, a secondelectron dlscharge detector, said detectors each including a cathode, an anode and a gride1e-' inent, connections whereby currents 0f'd1fferent intensity are supplied to said detecs tors, a plurality of means connected in the cathode anodecircuits of said detectors. for

in said seconddetector.

producing difierent direct current potentials Whichlare variable in response to thein-j tensity of the received current supplied to said detectorsrone of said means heingcommon to the cathode-anode circuits of both said detectors, and connections for impressing said difierent potentials uponthe grid elements of said detectors wherehy,.thegdii rect current potential applied to said heterodyne detector operates to prevent over1oad-- 

